1. Field of the Invention
This invention generally relates to drug-eluting coatings comprising one or more drugs in slow-dissolving polymorph having a controlled rate of release.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient. One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent.
Biomaterials with non-fouling characters are in special interest for their good biocompatibility. However, some of these materials provide an inadequate platform for delivery of drugs. Polyethylene glycol/poly(butylene terephthalate) (PEG/PBT) (PolyActive™) is one of the examples. Using PolyActive™ as a top coat for drug-eluting stent has repeatedly shown to reduce platelet deposition in in vitro models. This degradable polymer has shown to have a good mechanical property when coated onto stents. However, previous study indicated that the PolyActive™ could not be used as a matrix polymer because it is incapable of controlling the drug release.
Therefore, there is a need for a material having superior biocompatibility and nonfouling properties that is capable of forming a coating layer on a medical device, such as a stent. Moreover, there is a need for producing a coating made from these materials that provides for adequate release control of a therapeutic substance from the coating.
The embodiments of the present invention address the above described problems and needs.